Cam followers are used to translate the motion imparted from a cam to another component. For instance, the rotating motion of a cylindrical cam can be translated into linear motion by a cam follower. Cam followers are employed in engagement with cams in a vast number of mechanisms including internal combustion engines, valves, pumps, compressors, machine tools, fabric processing equipment, downhole rotary steerable systems, downhole agitators, and drilling machines such as the drilling machine disclosed in incorporated U.S. patent application Ser. No. 15/430,254 (the '254 Application), among other mechanisms.
Cam followers are categorized into two primary groups, including roller cam followers and non-roller cam followers. For roller cam followers, yoke mount or stud mount rolling members are employed. These rolling members are of the bushing type, or employ ball, roller, or needle bearings or a combination thereof. Non-roller cam followers are classified as knife edge, flat-face, or curved shoe, which is sometimes called mushroom. Table 1, below, sets forth various cam followers, including associated drawbacks.
TABLE 1RollerDrawbacks (roller)FixedDrawbacks (fixed)BushingFriction lower than Knife EdgeHigh contact stressFixed followers but and rapid wearhigher than other roller typesRoller Bearings/Many small movingFlat FaceHigher frictionNeedle Bearingsparts—In some forces due to applications require sliding contactseals and lubricationBall or Ball andMany small movingCurved Shoe Higher frictionRoller Bearingsparts—In some or Mushroomforces due to applications require sliding contactseals and lubrication
Thermally stable polycrystalline diamond (TSP), either supported or unsupported by tungsten carbide, and polycrystalline diamond compact (PDC or PCD) are sometimes used in tools, such as diamond tipped tools. Polycrystalline diamond, including thermally stable polycrystalline diamond and polycrystalline diamond compact, has been considered as contraindicated for use in the machining of ferrous metals, and other metals, metal alloys, composites, hardfacings, coatings, or platings that contain more than trace amounts of diamond catalyst or solvent elements, including cobalt, nickel, ruthenium, rhodium, palladium, chromium, manganese, copper, titanium, or tantalum. Further, this prior contraindication of the use of polycrystalline diamond extends to so called “superalloys”, including iron-based, cobalt-based and nickel-based superalloys containing more than trace amounts of diamond catalyst or solvent elements. The surface speeds typically used in machining of such materials typically ranges from about 0.2 m/s to about 5 m/s. Although these surface speeds are not particularly high, the load and attendant temperature generated, such as at a cutting tip, often exceeds the graphitization temperature of diamond (i.e., about 700° C.), which can, in the presence of diamond catalyst or solvent elements, lead to rapid wear and failure of components, such as diamond tipped tools. Without being bound by theory, the specific failure mechanism is believed to result from the chemical interaction of the carbon bearing diamond with the carbon attracting material that is being machined. An exemplary reference concerning the contraindication of polycrystalline diamond for diamond catalyst or solvent containing metal or alloy machining is U.S. Pat. No. 3,745,623, which is incorporated herein by reference in its entirety. The contraindication of polycrystalline diamond for machining diamond catalyst or solvent containing materials has long caused the avoidance of the use of polycrystalline diamond in all contacting applications with such materials.
Copper and titanium were not typically listed in the early General Electric documentation on diamond synthesis but have been added later. Relevant references include “Diamond Synthesis from Graphite in the Presence of Water and SiO2”; Dobrzhinetskaya and Green, II International Geology Review Vol. 49, 2007 and “Non-metallic catalysts for diamond synthesis under high pressure and high temperature”, Sun et al, Science in China August 1999.
Additional significant references that inform the background of the technology of this application are from the International Journal of Machine Tools & Manufacture 46 and 47 titled “Polishing of polycrystalline diamond by the technique of dynamic friction, part 1: Prediction of the interface temperature rise” and “Part 2, Material removal mechanism” 2005 and 2006. These references report on the dynamic friction polishing of PDC faces utilizing dry sliding contact under load with a carbon attractive steel disk. Key findings in these references indicate that polishing rate is more sensitive to sliding rate than load and that the rate of thermo-chemical reaction between the steel disk and the diamond surface reduces significantly as the surface finish of the diamond surface improves. The authors reference Iwai, Manabu & Uematsu, T & Suzuki, K & Yasunaga, N. (2001). “High efficiency polishing of PCD with rotating metal disc.” Proc. of ISAAT2001. 231-238. which concludes that the thermo-chemical reaction between the steel disk and the PDC face does not occur at sliding speeds below 10.5 m/s at a pressure of 27 MPa. These references are incorporated herein by reference, as if set out in full.
It would be desirable to provide a cam follower that offers a coefficient of friction (CoF) that is comparable to that CoF of roller bearing cam followers, without the attendant weaknesses associated with the small moving parts of roller bearing cam followers.